Glucagon is a peptide hormone produced by the alpha cells of the pancrease. Its actions are antagonistic to those of insulin and it is thus one of the important diabetogenic factors. We propose to prepare and characterize chemically modified forms of glucagon and to test their activity with regard to stimulation of adenylate cyclase and glycogenolysis. In this work we hope to prepare a derivative that will act as an antagonist to the native hormone. Another aspect of the project deals with identifying the glucagon receptor site by photoaffinity labelling. An aryl azide group has been covalently attached to the tryptophan residue of glucagon and will be used to label the membrane receptor site after photolysis.